Head and neck cancer is a group of cancers develop from the soft tissues, salivary gland, mucosa of the upper respiratory or digestive system covering the oral and nasal cavity. Radiotherapy is usually the standard treatment of Head and neck cancers. In the present study, investigators aim to study the prevalence of cervical-cranial vascular complications during the early stages in these Head and neck cancer patients receiving Radiotherapy. Investigators will also compare the results between Nasopharyngeal cancer and other Head and neck cancerpatients receiving Radiotherapy.

Population: Prospective cohort

Inclusion Criteria:

1. Age ≥20 years.
2. Head and neck cancer patient .
3. Had ever received radiation therapy (RT) ≦ 72 months before inclusion in the registry.
4. Had ≥ 1 brain images and cervical-cranial vascular studies between the end of RT and d date of enrolment.

Exclusion Criteria:

1. Age <20 years.
2. Patients not willing to sign the informed consent.

Population: Retrospective validation cohort

Inclusion Criteria:

1. Age ≥20 years.
2. Head and neck cancer patient.
3. Had ever received radiation therapy (RT) > 120 months before the adoption date of IRB at the participant site.
4. Had ≥ 2 brain images and cervical-cranial vascular studies between the end of RT and 6~10 years after RT, one within 5 years after RT, the other after 5 years after RT.

Exclusion Criteria:

1.Age <20 years.

The study population will comprise Head and neck cancer patients recruited in the prospective and retrospective cohorts. The Head and neck cancer patients in this study indicates those coded with ICD 10 (C00-13, C30-32). The coordinating center (Linkou medical center) will establish periodic communications through email and newsletters with participating sites (Keelung branch, Chia-yi branch, and etc.) to ensure data completeness and reduce the odds of loss-to follow-up of patients. We will aim to minimize data queries as much as possible, by prioritizing the completeness of the most relevant data for evaluating the main registry outcomes. We plan to follow up the patients until after 120 months after radiotherapy.